The present invention relates to an apparatus for determining concentration of ions in a solution.
Apparatus for determining concentration of ions which can operate for a long time by putting the internal solution of a comparison electrode into a cylindrical means for supporting electrodes, and having a construction as shown in FIG. 1 and FIG. 2 is well known.
FIG. 1 shows such an apparatus using a three-piece composite electrode of the single junction type and having a three-piece composite electrode (c) extending through an electrode packing (b) positioned in the lower portion of a hollow pipe (a) provided with an external thread and an electrode guard (d) threaded onto said pipe and surrounding the electrode (c). A KCl solution is introduced into the interior of the hollow pipe through an opening (f) formed in a protective cover (e) mounted on the end of said hollow pipe (a) at the other end from the packing (b). Although such a construction has the advantage that it is light and slim as a whole, it also has a defect that the insulation often breaks down because a pH electrode which requires a high insulation value such as 10.sup.8 .OMEGA. or more is immersed in a very permeable KCl solution. In addition, a back current or permeation of water to be tested may contaminate the comparison electrode and break down the internal electrode of the comparison electrode and thus give an abnormal indication in extreme cases when the pH electrode is immersed in water to be tested which has a high concentration of Cl.sup.- and SO.sub.3.sup.-. As to the maintenance, the exchanging of electrodes is difficult because all of the KCl solution contained in the means for supporting the electrodes must be drained or discarded, and moreover the entire electrode (c) must be exchanged when a glass electrode has been broken even though the comparison electrode does not have any abnormalities. This is very uneconomical.
FIG. 2 shows a prior art apparatus using a supporter of the double-junction type which can also be used as a comparison electrode and which has a double cylinder consisting of a closed hollow cylinder (g) and a further hollow pipe (h) extending coaxially therethrough, the internal pipe (h) having a glass electrode (i) fixedly mounted therein, an internal electrode (j) of the comparison electrode and an element (k) for determining temperature being positioned in the space between said external cylinder (g), and KCl solution being introduced into said space through an opening (l) in the upper portion of said external cylinder (g). In addition, a block (m) is provided at the lower end of cylinder (g) for fixing the glass electrode on the lower portion of said external cylinder (g) and has a liquid junction (n) extending therethrough, said block (m) having a cylinder (o) threaded thereon with a packing (m') between it and said cylinder (g), said cylinder (o) further having a packing (p) which also serves as a liquid junction at the lower portion thereof, the tip portion of the glass electrode (i) extending through said packing (p).
Although such a construction provides very effective insulation because said glass electrode (i) itself extends from a space separate from KCl solution, said glass electrode cannot be exchanged until the lowermost junction formed by the packing (p) is removed, and KCl solution contained in said cylinder (o) must be transferred to another vessel or discarded. Also, it is necessary that the caliber of said junction (n) be comparatively large because KCl solution must be transferred through the junction (n) from the space betwen said internal cylinder (h) and said external cylinder (g) to said lower cylinder (o) through said junction (n). Therefore, in practice, the advantage of the double-junction is greatly restricted. It takes a long time to transfer KCl solution from the space within cylinder (g) to the cylinder (o) if said junction (n) is made of ceramic or the like in order to increase the double-junction effect. Even though such a difficult problem of the junction could be solved, this construction nevertheless causes KCl solution to flow out of the system, and there is thus the possibility that the KCl solution in tube (g) will be lost even though KCl solution will remain in said cylinder (o). Under such a condition, it is impossible to determine the concentration of ions because the internal electrode (j) is no longer immersed.